The invention relates to a device for sequentially actuating a pair of valves. More particularly, this invention relates to a pressure control unit for actuating an inlet valve and an outlet valve to control the brake fluid of a wheel brake cylinder of a vehicle equipped with an anti-locking brake system. The inlet and outlet valves used to control the flow of brake fluid are required to be capable of mutually coordinated, non-overlapping operation at the most rapid speed attainable. That is to say, it is important that the normally closed outlet valve be opened only when the normally open inlet valve is closed. Piezoelectrically actuated valves with operating times less than 100 microseconds and locking forces of up to 7000 Newton are known. However, the adjustment stroke is short--approximately 0.07 mm. Typically, separate valves, each with an electromagnetic or piezoelectric adjusting element have been used for the inlet valve and outlet valve.
One object of the invention is to develop a device for coordinating the actuation of two interdependent valves, which reduces overlapping operation of the two valves to an acceptable amount, exhibits a sufficiently long adjustment stroke, and is also simple and inexpensive to produce.
According to the present invention, an apparatus is provided for actuating a pair of valves in sequence. A preferred embodiment of the apparatus includes a housing, a first and second valve mounted in the housing for movement in relation to the housing. The first valve includes a first tappet and a first spring means for yieldably biasing the first valve toward a normal position. The second valve includes a second tappet and a second spring means for yieldably biasing the second valve toward a normal position. The apparatus further includes an actuating member and a means for mounting the actuating member within the housing to selectably engage the first tappet, the second tappet, and a bearing point member. The bearing point member is fixed to the housing to lie on other than a line joining the two valve tappets. An actuator spring means is also provided for yieldably biasing the actuating member toward a normal position. The actuator spring means is situated intermediate a portion of the housing and the actuating element and in proximity to the second tappet. The actuator spring means has a spring force greater than the spring forces of each of the first and second spring means. An adjusting member is provided for tilting the actuating member to sequentially actuate the first and second valves. The actuating member is tiltable during a first adjustment stroke counter to the force of the first valve spring about a first axis of rotation defined by the bearing point fixed to the housing and by the compression spring in order to actuate the first valve and move the first tappet to a selected position. The actuating member is also tiltable during a second adjustment stroke counter to the force of the compression spring about a second axis of rotation defined by the bearing point fixed to the housing and by the second first tappet in order to actuate the second valve.
The actuating device of the present invention makes possible the actuation of both valves with one adjusting element. One conventional adjusting element is therefore dispensed with. Furthermore, overlapping operation of the two valves is reduced, because the second valve can be actuated only when the first has already reached its work position. Another advantage which may be mentioned, and which is particularly significant for piezoelectrical adjusting elements, is the definition of a lever arm between an adjusting element and the valve tappets for leveraging movement of the valve tappets which exhibits a ratio of 1:3. This leverage ratio is the same for both of the first and second valves.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purpose of illustration only, an embodiment in accordance with the present invention.